The evolution of inflators for automotive inflatable safety systems has resulted in the development of pressurized gas only inflators, propellant only inflators, and hybrid inflators. There are of course many design considerations for each of the above-noted types of inflators. In all three systems, two primary design considerations are that the air/safety bag must be expanded a predetermined amount in a predetermined amount of time in order to be operationally effective. As such, substantial development efforts have been directed to how the flow path is established between the inflator and the air/safety bag and how the subsequent flow is provided to the air/safety bag such that the above-identified objectives can be met. In hybrid inflators, which again require both a release of a stored, pressurized gas and an ignition of a gas and/or heat generating propellant, the manner of establishing the flow path to the air/safety bag and the manner of igniting the propellant must both be addressed in a way which meets the above-noted objectives.
Another important design consideration, particularly for inflators which utilize propellants, is the effect of the gases upon occupants of the automobile. That is, the gases within the expanded air/safety bag eventually permeate through the air/safety bag and are discharged to atmosphere. As such, it is desirable to have the gases within the air/safety bag be below a certain toxicity level. U.S. Pat. Nos. 3,690,695; 3,788,667; and 3,966,226 generally address this issue. Moreover, the appearance of the gases is important. As an example, one problem with current state-of-the-art hybrid inflators is that they produce, in the gas output stream, copious quantities of metal salt fumes (e.g., potassium chloride). This salt is present because an oxygen source (e.g., potassium perchlorate), has been added to the propellant formulation to minimize carbon monoxide production by oxidizing all carbon in the propellant to carbon dioxide. This salt fume is highly objectional in a crash situation because it has both physiological and psychological effects, imposed at a time of great physical and psychological stress. The salt fume in the post-crash automobile cabin drastically reduces visibility for the crash victims, and creates anxiety over the possibility of fire. Current hybrid inflators use propellants which typically contain more than 70% potassium perchlorate, which yields about 54% of the propellant weight as potassium chloride fume.
Since the weight of the automobile is an important design consideration in many instances today, so too then is the weight of the inflator. Moreover, due to the limited space available in many automotive designs, the size of the inflator is also an important design consideration. These types of factors have effectively rendered pressurized gas only inflators obsolete. In hybrid inflators, these types of considerations have resulted in many changes to the structure of the inflator and the materials selected for use in this structure. However, there continues to be a need for improvements in these areas.
Although the performance of a given inflator will of course influence the manufacturer's/supplier's position in the marketplace, system performance alone is no longer dispositive. That is, since inflatable safety systems are now being included in a large number of automobiles which will likely increase the number of manufacturers/suppliers of inflators, minimizing the cost of the inflator is becoming increasingly important to obtaining a competitive advantage. Consequently, it would be desirable to not only provide an inflator with competitive performance characteristics, but which is also cost competitive.